1. Subject of the Invention
The invention relates to a power module, having a printed circuit board core which contains at least one electronic power component embedded in an insulating layer, the core being arranged between two heat dissipation plates, wherein each heat dissipation plate has a metal outer layer and a metal inner layer electrically separated from said metal outer layer by a thermally conductive, electrically insulating intermediate layer, and electrode terminals of the at least one power component are guided out from the core via terminal lines.
2. Prior Art
In the case of power modules, which for example include IGBTs together with freewheeling diodes and which are intended to process high currents and voltages, which for example in the automotive field in the case of DC/AC converters in the case of electric drives lie in the region of 500 volts and 200 amperes and also thereabove, there is a need to keep the thermal resistance as low as possible, wherein the terminal lines are to be designed for high currents with very low inductance. When constructing modules of this type, what is known as “wire-bond” technology with Al wires and soldered connections is currently predominantly used. The individual components, such as IGBTs and diodes, are arranged here are on special substrates, for example DBC=direct bond copper technology), which for example consist of two copper layers, which are separated by a ceramic layer, such as Al2O3.
In order to meet the electrical and thermal requirements, the guidance of the terminal lines must be complex, wherein for example thick aluminium wires are used for the connection of gate and source contacts, arranged at the top, of IGBTs, however these wires, on account of their high coefficient of thermal expansion, tend to detach or rupture on account of what are known as “heel cracks” at bends. In the case of such arrangements the drain contacts of an IGBT, which are arranged on the opposite side, are soldered onto the substrate or are connected by press sintering. This substrate (DCB) is soldered onto a thick aluminium plate, which is arranged on a heat dissipation plate via a thermally conductive interface material. It has been demonstrated, however, that faults occur with relatively long periods of operation and are to be attributed to cycles of the performance and thermal stress and resultant different expansions of the components and cracks and material fatigue and manifest themselves for example in a detachment of the aluminium wires or in breaks of the chip or substrate.
The previously preferably used embeddings of power semiconductors are also characterised by a high self inductance of the wire connections, which leads to power losses and high heating, and by the use of costly substrates for the electrical insulation and heat transfer. In order to improve the efficiency of the cooling, solutions have also been created which provide double-sided cooling. Examples of such known power modules are presented and described inter alia in U.S. Pat. No. 8,102,047 B2, U.S. Pat. No. 7,514,636 B2 or U.S. Pat. No. 8,358,000 B2.
A power module of the type mentioned in the introduction is known for example from the article “High Power IGBT Modules Using Flip Chip Technology”, IEEE Transactions on Components and Packaging Technology, Vol. 24, No. 4, December 2001. In the case of this module, double-sided cooling is likewise provided, wherein power components, here two IGBTs and four diodes, are embedded between two DBC layers, which are in turn soldered onto heat sinks. The DBC substrate of the two layers consists of an Al2O3 layer 0.63 mm thick, which is covered on both sides by copper layers 0.3 mm thick. The drain contact of the IGBTs and the cathode terminals of the diodes are soldered by means of a tin/lead/silver solder to the lower DBC layer, and the source and the gate contacts of the IGBTs and the anode contacts of the diodes are soldered using the same solder to the upper DBC layer, wherein a flip-chip bonding technique is used. The terminal lines to the source and the gate contacts of the IGBTs and the anode contacts of the diodes are guided in the structured thin inner copper layer of the upper DBC layer. Although double-sided cooling is applied here, the problem of high-current lines to the power terminals (source of the IGBTs, anodes of the diodes), primarily in view of the self-inductances, remains unsolved.
It should be noted at this juncture that the terms “top” and “bottom” relate to the representations used conventionally, but do not specify the actual usage position of the modules. Furthermore, the power components under consideration here are primarily power semiconductors, such as IGBTs and freewheeling diodes, however this is not intended to be limiting, since either active or passive electronic/electrical components may also be part of the module.
The object of the invention lies in creating a power module of the type in question, in which the problem of heat dissipation or heat generation by line inductances in the case of power components embedded in a module is overcome economically.